MARTINSBURG, W.Va. — The wife of a Navy nuclear engineer pleaded guilty on Friday to taking part in a conspiracy to sell submarine secrets to a foreign country, bringing to a close an espionage case that mixed spycraft and politics with the travails of a suburban family.

Four days after her husband, Jonathan Toebbe, pleaded guilty in the case under a deal with the government, Diana Toebbe, a high school teacher in Annapolis, Md., acknowledged her part in a scheme to sell nuclear reactor secrets her husband had taken from the Navy, and will face a sentence of not more than three years, according to the terms of her agreement with the government. Her plea was entered during a hearing at a federal courthouse in Martinsburg.

In April 2020, the couple wrote to an undisclosed foreign government, which turned over the letter to the F.B.I. Investigators then set up a series of dead drops to ensnare Ms. Toebbe and Mr. Toebbe; he faces 12 to 17-and-a-half years in prison under the terms of his plea.

In the court proceeding Friday, prosecutors outlined how Ms. Toebbe served as a lookout while her husband deposited information in a dead drop set up by the F.B.I. Ms. Toebbe said she “knowingly and voluntarily joined a conspiracy with my husband, Jonathan Toebbe,” to attempt to sell government secrets to a foreign nation.

Ms. Toebbe appeared in court with short, graying hair that was neatly parted and wearing an orange prison uniform. She kept a white surgical mask on throughout the hearing. Chained at the wrist and ankles, Ms. Toebbe sat very still throughout the proceeding, responding sharply to questions from the magistrate judge. Her voice grew softer as she read her statement admitting how she had aided her husband.

While U.S. Attorney Jarod J. Douglas read the terms of her plea deal, Ms. Toebbe appeared to close her eyes or look down for an extended period of time, prompting her lawyer to tap her shoulder. She nodded to him in response.

Neither Ms. Toebbe’s husband nor her children were present at the hearing, and it did not appear that any family members were there to hear the guilty plea.

The couple’s plea deals will spare the government from a trial that could have risked exposing the foreign country involved in the plot — which officials have worked hard to keep secret. It might also have risked making public some of the material that the couple intended to provide to the foreign government.

Mr. Toebbe worked in the Washington Navy Yard, developing nuclear reactors for American submarines. While he had access to some of the nation’s most highly protected secrets, the exact nature of the material he tried to sell in exchange for a kind of cryptocurrency has not been revealed by the government.

 

Former students and colleagues at Annapolis’s elite Key School described Ms. Toebbe as increasingly frustrated with American politics and former President Donald J. Trump.

She also complained about her pay at the school. Her husband made a good government salary as a highly educated nuclear engineer, $153,737 a year. Ms. Toebbe had even stronger academic credentials, holding a Ph.D. from Emory University, but she earned less than some of her male colleagues, a source of friction she would express in front of her classes, according to former students.

And, people briefed on the investigation said, they thought the couple’s motivation was financial.

Under the terms of her plea agreement, Ms. Toebbe could face large fines and restitution to the government, although the government should not be able to take her house from her.

In an earlier court hearing over her detention, the government read from encrypted text messages between the couple that prosecutors said showed Ms. Toebbe’s alienation from the United States. The defense countered that Ms. Toebbe’s frustration with Mr. Trump was hardly treasonous and was in fact something many Americans shared.

The Toebbes have two school-aged children, who until the arrest of their parents, attended the school where their mother taught.

Some of the text messages revealed in court and discussions with people briefed on the case portrayed Ms. Toebbe as either an equal partner in the conspiracy or the person driving the plot forward.

But in Friday’s court hearing, Ms. Toebbe only acknowledged participating in the plan to try and sell secrets in the summer of 2021, when her husband was arranging with an undercover F.B.I. agent to deposit material in various dead drop sites. Prosecutors had video evidence of Ms. Toebbe serving as a lookout as Mr. Toebbe placed a memory card inside a peanut butter sandwich and left it for the undercover agent.

From the beginning of court proceeding, Mr. Toebbe positioned himself to take as much of the responsibility as he could — presumably an attempt to reduce the prison time his wife would serve. In jailhouse phone calls taped by the government, Mr. Toebbe told relatives his wife was innocent. And in his plea deal, Mr. Toebbe said it was he who wrote the letter to the foreign country and interacted with the undercover F.B.I. officer.

While he implicated her in the conspiracy, all he admitted was that she served as a lookout, what some outside observers said was the bare minimum, given that the F.B.I. had video of the couple at the dead drops they set up.

In the government’s view, since Mr. Toebbe held the security clearance and stole the material from the Navy, it was he who was the more guilty party.

While all the proceedings in the case, including Friday’s, have been overseen by Magistrate Judge Robert W. Trumble, the final sentencing of Ms. Toebbe will be conducted by Gina M. Groh, the district’s chief judge.